Many wireless communication terminal units, such as a personal digital assistant (PDA) and a cellular phone, have recently had an e-mail function as well as wire communication terminal units, such as a personal computer (PC).
These communication terminal units are generally equipped with a telephone directory in which a user can register information about his/her communication partners (hereinafter referred to as “registered information”). Each communication partner's registered information includes a pattern for informing the user of having received an e-mail from the communication partner (hereinafter referred to as “informing pattern”), which can be predetermined by the user for each communication partner, in addition to his/her name and e-mail address.
When receiving an e-mail from a sender, each communication terminal unit searches the telephone directory for an e-mail address that is the same as a source address recorded in the header of the e-mail. When finding the same address, the communication terminal unit informs the user of the reception of the e-mail and shows the sender's name on a display, in accordance with the informing pattern and name corresponding to the found e-mail address. It is very convenient for a user to be able to identify an e-mail sender by an informing pattern and name before displaying the body of the e-mail.
However, the source address recorded in the header of the e-mail is not always correct because an error may occur during transmission of the e-mail Consequently, there have been cases where although necessary information is stored in the telephone directory, the communication terminal unit can neither inform the user of the reception of the e-mail nor show the e-mail sender's name on the display because the communication terminal unit can not find an e-mail address that is the same as the received erroneous source address.